Study of Adsorption of H2 and CO2 on Distorted Structure of MOF-5 Framework; A Comprehensive DFT Study

Arjmandi, Mehrzad; Peyravi, Majid; Pourafshari Chenar, Mahdi; Jahanshahi, Mohsen; Arjmandi, Abolfazl

doi:10.22090/jwent.2018.01.007

Document Type : Original Research Paper

Authors

¹ Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

² Nanotechnology Research Institute, Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran

³ Department of Chemical Engineering, Mazandaran University of Science and Technology, Mazandaran, Iran

https://doi.org/10.22090/jwent.2018.01.007

Abstract

To investigate the adsorption property of H2 and CO2 on the organic ligand of C-MOF-5 (H2BDC) and T-MOF-5 (ZnO-doped H2BDC (ZnO-H2BDC)), Density functional theory (DFT) method was performed. First, the adsorption of ZnO on H2BDC resulted in examining binding energies, the charge transfer, density of states, dipole moments and adsorption geometries were investigated. The binding properties have been calculated and investigated theoretically for ZnO-doped H2BDC in terms of binding energies, band structures, Mulliken charges, and density of states (DOSs). According to obtained results, the H2BDC was strongly doped with ZnO. H2 and CO2 adsorption capacities for ZnO-doped H2BDC are significantly enhanced while there are low adsorption capacities for H2BDC. According to results, at least in the organic ligand of the MOF-5, the highest and lowest adsorption of CO2 (or H2) is attributed to the T-MOF-5 and C-MOF-5 respectively. Our calculations reveal that ZnO-doped H2BDC system (T-MOF-5) has much higher adsorption energy and higher net charge transfer value than pristine H2BDC (C-MOF-5). Also by changing in structure from cubic to tetragonal, the main site for H2 and CO2 adsorption was changed.

Keywords

Full Text

INTRODUCTION

In recent years, there has been an increasing interest in adsorption of various molecules [1-6] and developing gas storage systems for various applications such as CO₂ capture or H₂ storage [7-10]. By the same token, the metal-organic framework (MOF) family of materials have attracted particular attention due to their fascinating sorption properties [11-13]. In these materials, inorganic clusters (metals) and organic ligands can be connected to adopt a wide range of different structures, which open the possibility of tuning host-guest interactions in order to explore molecular sieving and adsorption properties unavailable in other materials.

One of the most important MOFs is Zn₄O₁₃C₂₄H₁₂ framework called as MOF-5, which was invented in 1999 [14]. This framework has potential applications for H₂ storage, CO₂ capture, and catalysts [15]. The MOF-5 consists of Zn₄O nodes which are linked to terephthalate anions (1,4-BDC = 1,4-benzenedicarboxylate) groups to form a porous material (Fig. 1(a)) [14]. It has been recognized that the MOF-5 occupies either cubic (C-MOF-5) or tetragonal (T-MOF-5) structure [16-20]. Cubic MOF-5 (with ultra-high BET surface area up to 3400 m²/g) has widely been synthesized by using a“diffusion” method [14] and tetragonal MOF-5 (with a medium surface area) can be synthesized via“direct mixing” approach [16].

The tetragonal MOF-5 is a distorted cubic MOF-5 [18]. Furthermore, this structure distortion was attributed to the presence of ZnO species extra phase and solvent in the pores [15,18-20]. Zhang and Hang Hu [15], showed that the composition (Zn_4.28O_12.8C₂₄H_11.3) of cubic MOF-5 sample is consistent with the stoichiometrical formula of Zn₄O₁₃C₂₄H₁₂. In contrast, the composition of the tetragonal MOF-5 sample with the calculated formula of Zn₄O₁₃C₂₄H_12.6(ZnO)_1.59(H₂O)_1.74 was very different from the stoichiometrical formula of Zn₄O₁₃C₂₄H₁₂, because ZnO and H₂O were present. The presence of H₂O might be due to the adsorption of H₂O when it was exposed to air. The formation of ZnO species is due to the reaction between zinc nitrate and H₂O₂ during the synthesis of tetragonal MOF-5.

In our previous work, we have shown that the T-MOF-5 had a lower surface area, lower porosity, smaller and more uniform pore size, and more ZnO molecule than C-MOF-5 [21]. Also in another work, we have synthesized and characterized the C-MOF-5 and T-MOF-5 as adsorbents for H₂ and CO₂ adsorption [22]. We found that the CO₂ adsorption capacity of C-MOF-5 is greater than that of T-MOF-5 and the H₂ adsorption capacity of C-MOF-5 is less than that of T-MOF-5 (at 298 K and 25 bar). This behavior was attributed to more ZnO units in T-MOF-5 than C-MOF-5.

According to literature, adsorption of small molecules in MOF-5 occurs first in a site near the Zn cluster in the large pores (site A’ in Fig. 1(b)) [23-27]. Sarmiento-Perez et al [28] introduced a similar site that is present in the smaller pore (site B’ in Fig. 1(b)). They showed that the site B’ in Fig. 1(b) is the main site for CO₂.

As reported in the literature, calculation of the chemical properties of MOF-5 using a representative fragment (such as an organic ligand) is in good agreement with the experimental results [29-31]. Considering the large size of cells in the MOF-5 structure for a quantum mechanics calculation, the model system should be decreased in size. The size reduction can be achieved by separating the H₂BDC linker. Accordingly, in this paper, we considered the adsorption behavior of CO₂ and H₂ molecules on the surface of C-MOF-5 (H₂BDC as a representative section) and T-MOF-5 (ZnO-H₂BDC as a representative section).

In the current study, we examined the adsorption of H₂ and CO₂ on the surface of H₂BDC and ZnO-H₂BDC (as a representative section of C-MOF-5 and T-MOF-5 nanostructures) using DFT calculations. First, we explored the geometric and electronic properties of H₂BDC surfaces upon decoration of ZnO (ZnO-H₂BDC) by examining binding energies, the charge transfer, density of states, dipole moments and adsorption geometries for the probable position. Then, the relaxed H₂BDC and ZnO-H₂BDC ligands are theoretically investigated for H₂ and CO₂ adsorption. In other words, we investigate in detail, the effect of more ZnO molecule in T-MOF-5 nanostructure than C-MOF-5 nanostructure on H₂ and CO₂ adsorption. We have achieved first-principles calculations to walk around the interaction behavior of the H₂ and CO₂ with H₂BDC and ZnO-H₂BDC.

Computational strategy

Geometry optimization, the density of states (DOS), and energy analyses were performed to investigate the adsorption phenomena using Gaussian 09 program package [32] with density functional theory (DFT) at B3LYP/6-31G (d,p) functional/basis set. The 6-31G(d,p) basis set is good for general calculations, besides the B3LYP density functional has been known appropriate for nano-structure studies. The temperature and pressure for all calculations were 298.15 K and 1.0 atm respectively.

A number of possible orientations are considered for H₂BDC, ZnO-H₂BDC, CO₂-H₂BDC, H₂-H₂BDC, CO₂-ZnO-H₂BDC, and H₂-ZnO-H₂BDC, but all input geometries resulted in optimization of limited structures, according to Fig. 2.

The adsorption Energy of ZnO on the H₂BDC is calculated by:

where is the energy of H₂BDC interacting with the ZnO and is the energy of a pristine H₂BDC, and is the energy of pristine ZnO. The interaction energy of CO₂ or H₂ (indexed by CO₂/H₂) with pristine H₂BDC and H₂BDC-ZnO are calculated by:

where and correspond to interaction energy of CO₂/H₂ with H₂BDC and ZnO-H₂BDC, and are energies of H₂BDC and ZnO-H₂BDC interacting with the CO₂/H₂, and is the energy of an isolated CO₂/H₂. All the mentioned energies of the equations are related to equivalently relaxed minimum energy structures. Also chemical potential () [33], hardness () [33], softness (S) [33] and electrophilicity () [33] are calculated by:

where E_HOMO and E_LUMO are the energies of HOMO and LUMO, respectively.

The charge transferring between CO₂/H₂ and the surface of both H₂BDC and ZnO-H₂BDC is calculated from the varying of the charge concentration on CO₂/H₂ after adsorption and an isolated spice. This calculation has been done by Mullikan charge analysis [34].

RESULTS AND DISCUSSION

Geometries of isolated pristine H₂BDC, ZnO-H₂BDC and their interaction with CO₂ and H₂ have optimized at B3LYP functional at 6-31G(d,p) basis set to allow them to be relaxed. Although the site C in Fig. 2 is the most attractive location for ZnO adsorption, but because this place will be occupied by ZnO molecules, as inorganic cluster, therefore in this study, to investigate the location of extra ZnO adsorption around the H₂BDC, the site A, B, and D in Fig. 2 were investigated. In this paper, we will discuss the strongest adsorption site and use the more stable configurations to further study (for all systems). Fig. 3 shows the optimized unit cell of H₂BDC and ZnO-H₂BDC. The values of adsorption energy, as well as some important parameters for all relaxed systems, are listed in Table 1. The geometric parameters of H₂BDC are in good agreement withthe already reported data [35]. According to results, the location D in Fig. 2 is the best location (in front of location A and B) for ZnO adsorption on H₂BDC (whit high adsorption energy, -111.5627 kJ/mol).

In order to study the adsorption of H₂ and CO₂ on H₂BDC and ZnO-H₂BDC, it is essential to note that there are two possible configurations for CO₂ (O end and C end) to be optimized. In this study, we used the more stable configuration. The interaction of H₂ and CO₂ molecules with H₂BDC and ZnO-H₂BDC on different positions (site A, B, and D in Fig. 2) has been studied using the above-mentioned method and let them be fully optimized. Fig. 4 shows the optimized unit cell of H₂-H₂BDC and CO₂-H₂BDC in three positions (site A, B, and D in Fig. 2). In this study, we found that there are two main sites for H₂ and CO₂ adsorption (named site A and site B respectively) on H₂BDC, while the E_ads for adsorption of H₂ and CO₂ on site D, is very little (as shown in Table 1).

In fact, considering that the organic ligand in MOF-5 is an appropriate representative [29-31], therefore Fig. 4 shows the adsorption behavior of H₂ and CO₂ on C-MOF-5. Accordingly as noted in the previous sections, the T-MOF-5 had more ZnO molecule than C-MOF-5. The differences between two nanocrystal structures bring about the different behavior in gas adsorption. To investigate the adsorption behavior of H₂ and CO₂ on T-MOF-5, the adsorption study on ZnO-H₂BDC (according to Fig. 3 (b)) was done. Fig. 5 shows the optimized unit cell of H₂-ZnO-H₂BDC and CO₂-ZnO-H₂BDC. The H₂ and CO₂ adsorption energies in ZnO-H₂BDC are -7.6125 and -45.6750 kJ/mol, respectively. According to results, we can conclude that, at least in the organic ligand of the MOF-5, the highest and lowest adsorption of H₂ (or CO₂) is attributed to the T-MOF-5 and C-MOF-5 respectively. Also by changing in structure from cubic to tetragonal, the main site for H₂ and CO₂ adsorption was changed. According to obtained results, the interaction of H₂ (or CO₂) on H₂BDC and ZnO-H₂BDC are in the range of physisorption. That’s while the interaction between ZnO and H₂BDC is intermediate between chemisorption and physisorption.

Although in this study, the investigations have been done on organic ligand of MOF-5, and according to the overall structure of MOF-5 has not been analyzed, however, the obtained results for H₂ adsorption on H₂BDC and ZnO-H₂BDC (as representative sections of C-MOF-5 and T-MOF-5) are in good agreement with experimental results obtained for H₂ adsorption on C-MOF-5 and T-MOF-5 [22]. Also, the experimental results for CO₂ adsorption on C-MOF-5 and T-MOF-5 [22] are in contrast to the obtained results in this study for CO₂ adsorption on H₂BDC and ZnO-H₂BDC (little difference in the same temperature and pressure).

As noted in the previous sections and according to our previous experimental results [21] with changing the structure from cubic to tetragonal, the pore size reduced from 8.67 Å to 6.3 Å. Because the kinetic diameter of hydrogen is very small, then it can be expected that changing the pores size from cubic to tetragonal has little effect on the H₂ diffusivity [19,20] and more effect on the bigger molecules (CO₂ in this study). Also, Sarmiento-Perez et al [28] reported that the primary step in the abnormal CO₂ adsorption in MOF-5 is due to synergic and significant contributions from all the three: the inorganic cluster, the organic linker and the 3-D structure of the nanopores. Therefore, the agreement between experimental results [22] and DFT theoretical results presented in this study for H₂ adsorption is attributed to the very small kinetic diameter of H₂. Accordingly, the difference between experimental results (complete structure) [22] and theoretical results presented in this work for CO₂ adsorption, is attributed to the bigger kinetic diameter of CO₂ and high impact of 3-D structure on the adsorption of CO₂. However, this difference does not violate the result of CO₂ adsorption (in this study).

We believe that the adsorption of ZnO on H₂BDC and also the adsorption of H₂ and CO₂ on H₂BDC and ZnO-H₂BDC can be interpreted by the amount of net charge transfer. The amounts of charge transferring between H₂BDC, ZnO, ZnO-H₂BDC, H₂, and CO₂ were simulated at the B3LYP functional at 6-31G(d,p) basis set. The Mulliken charge analysis is essential analysis for examination the net charge transferring in molecular systems. Table 1 shows the Mulliken charge of interacted ZnO with H₂BDC and alsointeracted H₂ and CO₂ with H₂BDC and ZnO-H₂BDC. In H₂-H₂BDC-A complex, H₂ detracts about 0.011e⁻charges to H₂BDC. Reverse transfer of charge achieved in ZnO-H₂BDC, CO₂-H₂BDC-B, CO₂-H₂BDC-D, H₂-H₂BDC-D, CO₂-ZnO-H₂BDC, and H₂-ZnO-H₂BDC complexes whereas ZnO loses about 0.107e⁻ charge from H₂BDC and CO₂ (also ZnO) loses about 0.101e⁻ (0.059e⁻) charge from ZnO-H₂BDC (also CO₂-H₂BDC) and H₂ (also ZnO) loses about 0.083e⁻ (0.058e⁻) charge from ZnO-H₂BDC (also H₂-H₂BDC). Also for CO₂-H₂BDC-B and CO₂-H₂BDC-D and H₂-H₂BDC-D complexes no net charge transfer occurs.

As shown in Table 1, significant changes in electronic properties were achieved during adsorption of ZnO on H₂BDC. Also, according to results of Table 1, there are no significant changes in the electronic properties of the pristine H₂BDC surface during interaction with H₂ and CO₂ but significant changes in electronic properties were achieved during adsorption of H₂ and CO₂ on ZnO-H₂BDC.

Supporting confirmation was found in the measured dipole moments (µD) of all systems. The dipole moment is related to the particular property of a molecule which considers data of electronic and geometrical properties [36]. The amounts of the size and structures of the dipole moment for H₂BDC on ZnO-H₂BDC and also for H₂ and CO₂ on the H₂BDC and ZnO-H₂BDC are listed in Table 1. Our computations reveal that when ZnO comes close to the H₂BDC, the size and directions of µD will change dramatically (from 0.0012 to 2.3339). Also, we found that during H₂ and CO₂ interaction for all systems, the µD is raised. The µD values of the interacted pristine H₂BDC with H₂ (site A), H₂ (site D), CO₂ (site B), and CO₂ (site D) are equal to 0.2828, 0.0096, 0.2563 and 0.0034 Debye, respectively. Also the alteration in the µD of ZnO-H₂BDC upon interaction with mentioned gas compounds increases in the order of CO₂ > H₂. Our results reveal that more dipole moment (4.5891 for CO₂-ZnO-H₂BDC and 3.6621 for H₂-ZnO-H₂BDC) corresponds to more adsorption energy which is in agreement with the results of charge analysis.

To more understand the electronic properties of the organic ligand of C-MOF-5 and T-MOF-5 during adsorption, the density of states (DOS) as the electron density of HOMO-LUMO was calculated for H₂BDC and ZnO-H₂BDC and also their complex was formed with H₂ and CO₂ molecule (see Table 1). Quantum mechanically, the interaction between two reactants takes place because of the interaction of frontier molecular orbitals [37]. HOMO and LOMU have the aptitude to contribute electrons and detract electrons, respectively. However, if a molecule has high HOMO energy, then it will be more unstable and contrariwise because of more reactivity [38,39]. The HOMO and LUMO energy orbitals for H₂BDC and ZnO-H₂BDC are found to be (-7.38 eV, -2.12 eV) and (-6.18 eV, -3.10 eV), respectively. After ZnO doping of H₂BDC (Zn-H₂BDC) and adsorption of H₂ and CO₂ molecule on the surface of H₂BDC and ZnO-H₂BDC, some changes occur in electronic properties.

The HOMO-LUMO energy gap (E_g) is one of the key parameters to recognize the stability as well as the conductivity of resulted adsorptions. Higher E_g results in more stability and less conductivity of resulted complex. The band gaps of the pristine H₂BDC and ZnO-H₂BDC as well as complex forms of CO₂-H₂BDC-B, CO₂-H₂BDC-D, H₂-H₂BDC-A, H₂-H₂BDC-D, H₂-ZnO-H₂BDC CO₂-ZnO-H₂BDC are calculated and are listed in Table 1. Adsorption behaviors of H₂ and CO₂ on H₂BDC and ZnO decorated H₂BDC (ZnO-H₂BDC) are mixed. For pristine H₂BDC, the band gap is almost the same on H₂ and CO₂ adsorption but for ZnO-H₂BDC-H₂ and ZnO-H₂BDC-CO_2, the band gap increases from 3.08 eV (for ZnO-H₂BDC) to 3.88 eV and 3.82 eV, respectively. The calculations revealed the highest E_g value for interacted ZnO-H₂BDC with H₂ and CO₂, which again correlates well with the high adsorption energies of H₂ and CO₂ on ZnO-H₂BDC compared to H₂BDC.

The change in E_g leads to changes in conductivity. The relationship between conductivity and E_g can be given by [40]:

where is the electric conductivity, k is the Boltzmann constant and T is the temperature. According to this equation, a small decrease in E_g leads to significantly higher electrical conductivities. According to results, pristine H₂BDC is not a good adsorbent for H₂ and CO₂ (particularly for H₂) molecule but adsorption of ZnO on H₂BDC significantly enhances its ability towards H₂ and CO₂adsorption (particularly for CO₂).

Next, we analyzed the densities of states (DOSs) as well as the electron density of HOMO-LUMO to realize how the adsorption of ZnO affects the electronic structure of H₂BDC. Fig. 6 plots the DOSs as well as the electron density of HOMO-LUMO for H₂BDC and ZnO-H₂BDC near the Fermi level (E_F). According to Table 1 and Fig. 5, for pristine H₂BDC, the Fermi level (E_FL) is slightly changed from -4.75 eV to -4.79 eV, -4.76 eV, -4.79 eV and -4.75 eV for CO₂-H₂BDC-B, CO₂-H₂BDC-D, H₂-H₂BDC-A, and H₂-H₂BDC-D, respectively. For ZnO-H₂BDC, the E_FL is changed a lot from -4.64 eV to -3.92 eV and -4.08 eV for CO₂-ZnO-H₂BDC and H₂-ZnO-H₂BDC, respectively. After comparing the DOS of H₂BDC and ZnO-H₂BDC with that of their interacted forms, we found that the ZnO doping of H₂BDC (ZnO-H₂BDC) causes a significant shift of the occupied orbitals of H₂BDC to high energy levels and observed some change evidence of hybridization in the case of ZnO-H₂BDC systems.

Also according to Fig. 6, The HOMO and LUMO in H₂BDC are uniformly dispersed over the entire skeleton of the pristine organic ligand. The effect of H₂ and CO₂ adsorption on H₂BDC is almost negligible. The decoration of ZnO on H₂BDC brings quite significant changes regarding both energies and densities. Adsorption of ZnO on the surface of H₂BDC increases the energy of HOMO but decreases the energy of LUMO which ultimately results in a decrease in the band gap (from 5.26 to 3.08).

The effect of ZnO doping of H₂BDC (ZnO-H₂BDC) and H₂ and CO₂ adsorption on H₂BDC and ZnO-H₂BDC, and on the electronic structure of the H₂BDC, ZnO-H₂BDC, CO₂-H₂BDC-B, H₂-H₂BDC-A, CO₂-H₂BDC-D, H₂-H₂BDC-D, CO₂-ZnO-H₂BDC, and H₂-ZnO-H₂BDC can be seen in MEP map, shown in Fig. 7. According to Fig. 7(a and b), the pristine H₂BDC has symmetrical potential (due to symmetrical structure) and ZnO atom has positive potential. Also, as shown in Fig. 7(c,d,e and f) the adsorption of H₂ and CO₂ molecules on H₂BDC does not affect on the intensification of positive or negative charge of H₂BDC (particularly for adsorption on-site D Fig. 7(e and f)). For ZnO-H₂BDC, the Zn and O atoms have positive and negative potential (respectively) whereas the atoms in the H₂BDC have almost neutral potential. The negative and positive potential on H₂BDC was changed in ZnO decorated H₂BDC (ZnO-H₂BDC). Upon adsorption of H₂ and CO₂ (particularly for CO₂) molecule on ZnO-H₂BDC, the negative potential is regenerated on the H₂BDC. The MEP analysis also shows that upon H₂ and CO₂ adsorption, the position of positive potential also shifts to close around of Zn.

We have also calculated the global indices of reactivity for CO₂, H₂, ZnO, H₂BDC, ZnO-H₂BDC, CO₂-H₂BDC-B, CO₂-H₂BDC-D, CO₂-ZnO-H₂BDC, H₂-H₂BDC-A, H₂-H₂BDC-D and H₂-ZnO-H₂BDC systems in order to evaluate how the adsorption of ZnO affects the chemical properties of H₂BDC for H₂ and CO₂ adsorption (Table 2). The energies of LUMO correspond to the electron affinity (define as A) whereas the energies of HOMO can approximately be taken equivalent to ionization potential (define as I) [33]. The ionization potential (I) for pristine H₂BDC is very high and does not decrease upon adsorption of H₂ and CO₂. The decoration of the H₂BDC with ZnO causes a reduction in ionization potential. Also, the ionization potential decreases when H₂ and CO₂ molecules are adsorbed on ZnO decorated H₂BDC. The band gap represents the softness (S) or hardness (η) of a compound. A compound with large band gap is expected to be hard, and conversely. After decoration of the H₂BDC with ZnO, the band gap decreases from 2.63 to 1.54 and it is expected that these complexes (ZnO-H₂BDC) are very soft. According to Table 2, after adsorption of H₂ and CO₂ on H₂BDC the softness values approximately remain unchanged, but after adsorption of H₂ and CO₂ on ZnO-H₂BDC, the softness values declined. The increase in chemical reactivity is electrophilic in nature because the electrophilicity of ZnO-H₂BDC (6.990 eV) is higher than the H₂BDC (4.289 eV).

CONCLUSIONS

We have shown theoretically for the first time that how H₂ and CO₂ adsorption on cubic and tetragonal structure of MOF-5 are different. Accordingly, we optimized the geometries for pristine H₂BDC as well as ZnO doped H₂BDC and their interaction with H₂ and CO₂. Firstly we investigated the possible positions of ZnO on H₂BDC. Among the three sites around H₂BDC (site A, B, and D) for ZnO adsorbed H₂BDC, the site D is more stable than site A and B. According to obtained results, at least in the organic ligand of the MOF-5, the highest and lowest adsorption of CO₂ and H₂ is attributed to the T-MOF-5 and C-MOF-5 respectively. Also among the three sites around H₂BDC (site A, B, and D) by a change in structure from cubic (H₂BDC) to tetragonal (ZnO-H₂BDC), the main site for H₂ and CO₂ adsorption was changed from A and B to D site. Our calculations determine that ZnO-H₂BDC system (as a representative section of T-MOF-5) has much higher adsorption energy, and higher net charge transfer value than pristine H₂BDC (as a representative section of C-MOF-5).

This is a qualitative, exploratory study in which the authors are laying the groundwork for future researches on this subject. It is exploratory because no other researches have been conducted on this specific subject.

ACKNOWLEDGEMENT

The authors acknowledge Iran Nanotechnology Initiative Council for financial support.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of interest regarding the publication of this manuscript.

References

1. Abbasi A, Sardroodi JJ, Ebrahimzadeh AR. Chemisorption of CH2O on N-doped TiO2 anatase nanoparticle as modified nanostructure media: A DFT study. Surf Sci. 2016;654(Supplement C):20-32.

2. Abbasi A, Jahanbin Sardroodi J. N-doped TiO2 anatase nanoparticles as a highly sensitive gas sensor for NO2 detection: insights from DFT computations. Environ Sci Nano. 2016;3(5):1153-64.

3. Abbasi A, Jahanbin Sardroodi J. Modified N-doped TiO2 anatase nanoparticle as an ideal O3 gas sensor: Insights from density functional theory calculations. Comput Theor Chem. 2016;1095(Supplement C):15-28.

4. Abbasi A, Sardroodi JJ. A novel strategy for SOx removal by N-doped TiO2/WSe2 nanocomposite as a highly efficient molecule sensor investigated by van der Waals corrected DFT. Comput Theor Chem. 2017;1114(Supplement C):8-19.

5. Abbasi A, Jahanbin Sardroodi J. Van der Waals corrected DFT study on the adsorption behaviors of TiO2 anatase nanoparticles as potential molecule sensor for thiophene detection. Journal of Water and Environmental Nanotechnology. 2017;2(1):52-65.

6. Abbasi A, Jahanbin Sardroodi J, Rastkar Ebrahimzadeh A. TiO2/Gold nanocomposite as an extremely sensitive molecule sensor for NO2 detection: A DFT study. Journal of Water and Environmental Nanotechnology. 2016;1(1):55-62.

7. Marco-Lozar JP, Juan-Juan J, Suárez-García F, Cazorla-Amorós D, Linares-Solano A. MOF-5 and activated carbons as adsorbents for gas storage. Int J Hydrogen Energy. 2012;37(3):2370-81.

8. Saha D, Deng S. Synthesis, characterization and hydrogen adsorption in mixed crystals of MOF-5 and MOF-177. Int J Hydrogen Energy. 2009;34(6):2670-8.

9. Saha D, Wei Z, Deng S. Hydrogen adsorption equilibrium and kinetics in metal–organic framework (MOF-5) synthesized with DEF approach. Sep Purif Technol. 2009;64(3):280-7.

10. Lou W, Yang J, Li L, Li J. Adsorption and separation of CO2 on Fe(II)-MOF-74: Effect of the open metal coordination site. J Solid State Chem. 2014;213(Supplement C):224-8.

11. Wang B, Côté AP, Furukawa H, O’Keeffe M, Yaghi OM. Colossal cages in zeolitic imidazolate frameworks as selective carbon dioxide reservoirs. NATURE. 2008;453:207.

12. Caskey SR, Wong-Foy AG, Matzger AJ. Dramatic Tuning of Carbon Dioxide Uptake via Metal Substitution in a Coordination Polymer with Cylindrical Pores. J Am Chem Soc. 2008;130(33):10870-1.

13. Llewellyn PL, Bourrelly S, Serre C, Vimont A, Daturi M, Hamon L, et al. High Uptakes of CO2 and CH4 in Mesoporous Metal—Organic Frameworks MIL-100 and MIL-101. LANGMUIR. 2008;24(14):7245-50.

14. Li H, Eddaoudi M, O'Keeffe M, Yaghi OM. Design and synthesis of an exceptionally stable and highly porous metal-organic framework. NATURE. 1999;402:276.

15. Zhang L, Hu YH. Structure distortion of Zn4O13C24H12 framework (MOF-5). Materials Science and Engineering: B. 2011;176(7):573-8.

16. Huang L, Wang H, Chen J, Wang Z, Sun J, Zhao D, et al. Synthesis, morphology control, and properties of porous metal–organic coordination polymers. Microporous Mesoporous Mater. 2003;58(2):105-14.

17. Kaye SS, Dailly A, Yaghi OM, Long JR. Impact of Preparation and Handling on the Hydrogen Storage Properties of Zn4O(1,4-benzenedicarboxylate)3 (MOF-5). J Am Chem Soc. 2007;129(46):14176-7.

18. Hafizovic J, Bjørgen M, Olsbye U, Dietzel PDC, Bordiga S, Prestipino C, et al. The Inconsistency in Adsorption Properties and Powder XRD Data of MOF-5 Is Rationalized by Framework Interpenetration and the Presence of Organic and Inorganic Species in the Nanocavities. J Am Chem Soc. 2007;129(12):3612-20.

19. Arjmandi M, Pakizeh M. Mixed matrix membranes incorporated with cubic-MOF-5 for improved polyetherimide gas separation membranes: Theory and experiment. J Ind Eng Chem. 2014;20(5):3857-68.

20. Arjmandi M, Pakizeh M, Pirouzram O. The role of tetragonal-metal-organic framework-5 loadings with extra ZnO molecule on the gas separation performance of mixed matrix membrane. Korean J Chem Eng. 2015;32(6):1178-87.

21. Arjmandi M, Pakizeh M. Effects of washing and drying on crystal structure and pore size distribution (PSD) of Zn4O13C24H12 framework (IRMOF-1). Acta Metallurgica Sinica (English Letters). 2013;26(5):597-601.

22. Arjmandi M, Pakizeh M. AN EXPERIMENTAL STUDY OF H2 AND CO2 ADSORPTION BEHAVIOR OF C-MOF-5 AND T-MOF-5: A COMPLEMENTARY STUDY. Braz J Chem Eng. 2016;33:225-33.

23. Walton KS, Millward AR, Dubbeldam D, Frost H, Low JJ, Yaghi OM, et al. Understanding Inflections and Steps in Carbon Dioxide Adsorption Isotherms in Metal-Organic Frameworks. J Am Chem Soc. 2008;130(2):406-7.

24. Dubbeldam D, Frost H, Walton KS, Snurr RQ. Molecular simulation of adsorption sites of light gases in the metal-organic framework IRMOF-1. Fluid Phase Equilib. 2007;261(1):152-61.

25. Martin-Calvo A, Garcia-Perez E, Manuel Castillo J, Calero S. Molecular simulations for adsorption and separation of natural gas in IRMOF-1 and Cu-BTC metal-organic frameworks. PCCP. 2008;10(47):7085-91.

26. De Toni M, Pullumbi P, Coudert F-X, Fuchs AH. Understanding the Effect of Confinement on the Liquid−Gas Transition: A Study of Adsorption Isotherms in a Family of Metal−Organic Frameworks. The Journal of Physical Chemistry C. 2010;114(49):21631-7.

27. Fairen-Jimenez D, Seaton NA, Düren T. Unusual Adsorption Behavior on Metal−Organic Frameworks. LANGMUIR. 2010;26(18):14694-9.

28. Sarmiento-Perez RA, Rodriguez-Albelo LM, Gomez A, Autie-Perez M, Lewis DW, Ruiz-Salvador AR. Surprising role of the BDC organic ligand in the adsorption of CO2 by MOF-5. Microporous Mesoporous Mater. 2012;163(Supplement C):186-91.

29. Hu YH, Zhang L. Amorphization of metal-organic framework MOF-5 at unusually low applied pressure. PHYS REV B. 2010;81(17):174103.

30. Yang L-M, Vajeeston P, Ravindran P, Fjellvåg H, Tilset M. Theoretical Investigations on the Chemical Bonding, Electronic Structure, And Optical Properties of the Metal−Organic Framework MOF-5. Inorg Chem. 2010;49(22):10283-90.

31. Petrova T, Michalkova A, Leszczynski J. Adsorption of RDX and TATP on IRMOF-1: an ab initio study. Struct Chem. 2010;21(2):391-404.

32. Frisch M, Trucks G, Schlegel H, Scuseria G, Robb M, Cheeseman J, et al. 09, Revision D. 01, Gaussian. Inc, Wallingford, CT. 2009.

33. Koopmans T. Ordering of wave functions and eigenenergies to the individual electrons of an atom. Physica. 1933;1(1):104-13.

34. Mulliken RS. Electronic Population Analysis on LCAO–MO Molecular Wave Functions. I. The Journal of Chemical Physics. 1955;23(10):1833-40.